Polymer for carbon fiber precursor

ABSTRACT

There is provided a carbon fiber precursor polymer which is composed of a polymer comprising 50 wt % or greater of an acrylonitrile component, wherein the isotactic triad proportion of the acrylonitrile structural chain composed of the acrylonitrile component is 35 mole percent or greater based on the total triad proportion of the acrylonitrile structural chain composed of the acrylonitrile component, the carbon fiber precursor polymer allowing flame retardant treatment to be carried out slowly from a low temperature range, and having satisfactory flame retardant properties including low heat generation.

TECHNICAL FIELD

The present invention relates to a carbon fiber precursor polymer whichallows production of carbon fibers, to a carbon fiber precursor obtainedby spinning the polymer, and to a flame retardant carbon fiber precursorobtained by heat treatment thereof. More specifically, the inventionrelates to a carbon fiber precursor polymer and carbon fiber precursorwhich yield high quality, high performance carbon fibers wherein thetemperature for flame retardant treatment can be lowered by controllingthe stereoregularity of the acrylonitrile repeating unit of thepolyacrylonitrile, in order to reduce the energy and time required forflame retardant treatment, and wherein no fusion or thermaldecomposition occurs between fibers even as carbonization proceeds.

BACKGROUND ART

Carbon fibers generally have excellent mechanical properties andespecially high specific strength and specific modulus, and aretherefore widely used as strength modifiers for various reinforcingmaterials in aerospace applications, leisure goods, industrial materialsand the like. Because of their superior mechanical properties, they havepotential application for reducing automobile weight and are receivingincreasing attention as an important advance in solving the urgentproblem of reducing carbon dioxide.

Such carbon fibers are produced by subjecting precursor organic polymerfibers to flame retardant treatment, firing and carbonization in thepresence of oxygen. Various precursors may be mentioned, includingcellulose, phenol resins, polyvinyl alcohol, vinylidene chloride, pitch,poliyacrylonitrile (hereinafter abbreviated as “PAN”) and the like.Carbon fibers derived from PAN-based fibers are particularly superior intheir dynamic properties such as specific strength and specific modulus,and because they can be produced with uniform and stable quality andperformance, they are mass produced on an industrial scale.

When PAN-based fibers are subjected to flame retardant treatmentfollowed by carbonization to produce carbon fibers, it has normally beennecessary to carry out heat treatment for a long period in ahigh-temperature oxidizing atmosphere of 200-400° C., as the conditionsfor flame retardant treatment. This is because flame retardant treatmentof the precursor PAN-based fibers attempted all at once in a shortperiod at a temperature of 500° C. or above produces a sudden exothermicdecomposition reaction which results in self combustion anddecomposition of the polymer, preventing formation of the desired carbonskeleton. Furthermore, prolonged high-temperature heat treatment is notonly problematic in economic terms because of high energy consumptionand low productivity, but also in terms of quality from the standpointof strength reduction due to fusion between single fibers, and in termsof process flow since filament breakage readily occurs at hightemperature, for which reasons a need exists for industrial improvement.

Various proposals have been set forth in the prior art in order to avoidsuch problems. For example, there has been proposed the use of aPAN-based precursor obtained by copolymerization of a specific amount ofa polymerizable unsaturated carboxylic acid ammonium salt (for example,see patent documents 1 and 2) and the use of a precursor which is PANobtained by copolymerization of a long-chain alkyl ester of apolymerizable unsaturated carboxylic acid (for example, see patentdocument 3).

These precursors exhibit certain effects of promoting flame retardantreaction, but the low copolymerizability of unsaturated carboxylic acidsoften leads to blocking of the copolymer. In addition, a high proportionof a carboxylic acid component with poor heat resistance is adisadvantage in that it can lead to lower yields as a result of thermaldecomposition during the flame retardant step following thepolymerization step.

On the other hand, it has been demonstrated that copolymerization ofα-chloroacrylonitrile with acrylonitrile can drastically shorten theflame retardant time and solve the problem of poor productivity (forexample, see patent documents 4 and 5). Still, a large amount of thecostly α-chloroacrylonitrile component must be used for copolymerizationin order to adequately shorten the flame retardant time, thus presentingan economic drawback which counteracts with the improvement inproductivity.

It has also been disclosed that using a terpolymer incorporatingitaconic acid and an acrylamide-based monomer with acrylonitrile canimprove the flame retardant properties (for example, see patent document6), but in addition to the difficulty of obtaining a homogeneouscopolymer with three different monomers, any excess of itaconic acid canresult in a violent exothermic reaction producing damage in the fiberstructure, while an excess of the acrylamide monomer can produce fiberfusion and can thereby complicate control of the copolymer compositionand influence productivity. Other proposals include usinghydroxymethylene (for example, see patent document 7), halogenated alkylesters of unsaturated carboxylic acids (for example, see patent document8) and silicon- or fluorine-containing unsaturated monomers (forexample, see patent document 9) as copolymerization components, but noneof these have exhibited satisfactory effects from a cost and performancestandpoint.

On the other hand, research is also progressing in the area of flameretardant reaction for PAN-based fibers. For example, flame retardantreaction for PAN-based fibers is now known to be initiated by oxidationand cyclization of adjacent nitrile skeletons (for example, seenon-patent document 1).

In addition, it has been reported through past research that for suchthermally induced reactions, the polymer microstructure, andspecifically the stereoregularity of the polymer main chain described byits tacticity, can affect the reaction temperature and reaction rate.For example, it has been demonstrated that formation of an imineskeleton from nitrile groups by heating proceeds preferentially at lowtemperature with isotactic chains rather than with atactic orsyndiotactic chains (for example, see non-patent documents 2 and 3).

Copolymers of PAN with no stereostructure regularity, i.e. atactic PAN,obtained by ordinary radical polymerization have been used asconventional carbon fiber precursor polymers and carbon fiberprecursors. Still, no literature or reports have been published to datewhich examine the use of a single PAN with stereostructure regularity,i.e. isotactic PAN, as a carbon fiber precursor polymer and carbon fiberprecursor with excellent flame retardant reactivity.

[Patent document 1]

Japanese Unexamined Patent Publication SHO No. 48-63029

[Patent document 2]

Japanese Examined Patent Publication SHO No. 58-48643

[Patent document 3]

Japanese Unexamined Patent Publication SHO No. 61-152812

[Patent document 4]

Japanese Examined Patent Publication SHO No. 49-14404

[Patent document 5]

Japanese Examined Patent Publication HEI No. 6-27368

[Patent document 6]

Japanese Unexamined Patent Publication HEI No. 11-117123

[Patent document 7]

Japanese Unexamined Patent Publication SHO No. 52-53995

[Patent document 8]

Japanese Unexamined Patent Publication SHO No. 52-55725

[Patent document 9]

Japanese Unexamined Patent Publication HEI No. 2-14013

[Non-patent document 1]

W. Watt et al., “Proceedings of the International Carbon FiberConference London”, Paper No. 4, 1971

[Non-patent document 2]

N. A. Kobasova et al., “VYSOKOMOLEKULYAR NYE SOEDINENIYA SERIYA A”,Russia, 13(1), 1971, P. 162-167

[Non-patent document 3]

M. A. Geiderikh, “VYSOKOMOLEKULYAR NYE SOEDINENIYA SERIYA A”, Russia,15(6), 1973, P. 1239-1247.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve the aforementionedproblems of the prior art by providing a carbon fiber precursor polymerand precursor which allow the temperature for the flame retardant stepto be essentially lowered in order to inhibit fusion or thermaldecomposition between fibers, without using large amounts of anexpensive or special purpose monomer.

BEST MODE FOR CARRYING OUT THE INVENTION

The carbon fiber precursor polymer of the invention must be composed ofa polymer comprising 50 wt % or greater of an acrylonitrile component,and the isotactic triad proportion of the acrylonitrile structural chaincomposed of the acrylonitrile component must be 35 mole percent orgreater based on the total triad proportion of the acrylonitrilestructural chain composed of the acrylonitrile component.

By using this manner of carbon fiber precursor polymer, it is possibleto accomplish flame retardant treatment at a lower temperature andshorter time compared to carbon fiber production using conventionalatactic PAN-based polymers, and thus not only significantly reduceenergy usage but also overcome quality problems such as strengthreduction due to fusion between single fibers, and process flow problemssuch as filament breakage.

A carbon fiber precursor polymer according to the invention is apremolding polymer in the form of a mass or pellets after polymerizationof a polymer containing 50 wt % or greater of the acrylonitrilecomponent but before molding into the desired shape, and a carbon fiberprecursor according to the invention refers to the state afterpolymerization of the polymer containing 50 wt % or greater of theacrylonitrile component, and after molding into the form of a filamentthrough a spinning process such as wet spinning, dry-wet spinning or dryspinning. In other words, the latter refers to the state before flameretardant treatment and heat carbonization treatment.

The carbon fiber precursor polymer of the invention must be composed ofa polymer comprising 50 wt % or greater of an acrylonitrile component,because if the acrylonitrile component is present at less than 50 wt %,an adequate effect for improvement of the flame retardant property willnot be exhibited in comparison to using an atactic PAN-based copolymer,and it will therefore be difficult to achieve the object of theinvention.

The carbon fiber precursor polymer may be a simple polymer ofstereoregular isotactic PAN wherein the isotactic triad proportion is 35mole percent or greater, or it may be a mixture of two or more differentpolymers copolymerizing 50 wt % or greater of isotactic PAN, or acopolymer obtained by copolymerization which produces 50 wt % or greaterof isotactic PAN.

The carbon fiber precursor polymer of the invention preferably comprisesa copolymer composed of an acrylonitrile component, acrylic acid-basedcompound component and acrylic acid ester-based compound component asthe main copolymerizing components, preferably wherein the acrylonitrilecomponent constitutes at least 80 wt % of the copolymer and the totalweight percentage of the acrylic acid-based compound component and theacrylic acid ester-based compound component is greater than 0% and lessthan 20%.

Here, “main” means that the total of the aforementioned three components(acrylonitrile component, acrylic acid-based compound component andacrylic acid ester-based compound component) constitutes at least 80 wt% and more preferably at least 90 wt % of the total copolymer component.

The acrylonitrile component preferably constitutes at least 80 wt % ofthe copolymer, which allows the hexagonal plane layer of the carbonfiber precursor to form adequately for supply to the flame retardantstep, and also results in adequate performance of the carbon fiberproduct. The acrylonitrile component content is preferably 90 wt % orgreater.

The copolymer preferably has a total weight percentage of the acrylicacid-based compound component and the acrylic acid ester-based compoundcomponent of greater than 0% and less than 20%, a range which willlikewise allow the hexagonal plane layer of the carbon fiber precursorto form adequately for supply to the flame retardant step, while alsoresulting in adequate performance of the carbon fiber product.

In the polymer of the invention, the proportion of the isotactic triadcontent (mm triad %) of the acrylonitrile structural chain composed ofthe acrylonitrile component, relating to the acrylonitrile-derived peakas estimated by ¹³C-NMR, must be at least 35 mole percent based on thetotal triad proportion of the acrylonitrile structural chain composed ofthe acrylonitrile component. If it is not within this range, theincreased distance between adjacent cyano groups in the structural chainwill impede formation of the hexagonal plane layer of the carbon fiberprecursor when supplied to the flame retardant step, and the dynamicstrength of the carbon fibers obtained as the final product will beinsufficient. The isotactic triad content (mm triad %) is preferably atleast 65 mole percent based on the total triad proportion of theacrylonitrile structural chain composed of the acrylonitrile component.

The isotactic triad content (mm triad %) is the proportion of threecontiguous repeating units (a triple structural chain) in an additionpolymerization type polymer wherein all of the adjacent monomer unitside chains are in the meso (m) configuration.

Other types of triads include heterotactic triads (mr) and syndiotactictriads (rr). Here, “r” indicates a racemic configuration.

In other words, the isotactic triad content is the proportion of mmamong the mm, mr and rr triads.

If the triad content (mm %) is less than 35 mole percent, the PANspatial configuration will not exhibit an adequate effect on the flameretardant property, resulting in substantially little distinction fromatactic PAN.

According to the invention, other components may also be copolymerized,preferably at less than 50 wt %, so long as the effect of the inventionis exhibited, and although any conventional publicly knowncopolymerizable unsaturated compounds may be used, there are preferredunsaturated carboxylic acids and/or unsaturated carboxylic acid esters,and especially acrylic acid, methacrylic acid, itaconic acid and/ortheir alkyl esters.

As alkyl esters there are particularly preferred esters having C1-6alkyl groups, such as one or more groups selected from among methyl,ethyl, propyl, isopropyl, n-butyl, i-butyl, t-butyl and cyclohexyl.

As other copolymerizing components there are preferably usedacrylonitrile components, polar vinyl compounds such as acrylicacid-based compounds, acrylic acid ester-based compounds,methacrylonitrile, vinyl acetate, acrylamide, maleic anhydride andN-vinylpyrrolidone, and aromatic vinyl compounds such as styrene,vinylpyridine and vinylimidazole. These copolymerizing components may beused alone or in combinations, and preferably one or more compounds areselected from the group consisting of polar vinyl monomers includingacrylic acid, methacrylic acid, itaconic acid and their alkyl esters,methacrylonitrile, vinyl acetate, acrylamide, maleic anhydride andN-vinylpyrrolidone, and aromatic vinyl compounds such as styrene,vinylpyridine and vinylimidazole, among which acrylonitrile components,acrylic acid-based compounds and acrylic acid ester-based compounds areparticularly preferred for use.

Copolymerization of these components yields a random copolymer withacrylonitrile in a random arrangement, or a block copolymer formingblocks of acrylonitrile chains and other copolymerizing componentchains.

Another role of the other copolymerizing components is to inhibitself-heating which occurs with intramolecular cyclization during theflame retardant treatment in order to attenuate thermal damage to thecarbon fiber precursor, but excessive copolymerization of anothercopolymerizing component for this purpose can sometimes lead to reducedperformance of the carbon fibers, and therefore when anothercopolymerizing component is used it is preferably present at less than20 mole percent of the carbon fiber precursor polymer.

The process for production of a carbon fiber precursor polymer accordingto the invention is not particularly restricted so long as it is aprocess allowing production of isotactic PAN, and examples of effectiveprocesses include the solid-phase photopolymerization at low temperature(−78° C.) using a urea/monomer clathrate complex as reported by D. M.White et al. in J. Am. Chem. Soc., 1960, 82, 5671,

an anionic polymerization process employing organic magnesium or thelike as the reaction initiator (Y. Nakano et al., Polym. Int., 1994,35(3), 249-55), or a radical polymerization process employing magnesiumchloride or the like as a molecular template/carrier (H. Kuwahara etal., Polymer Preprints, 2002, 43(2), 978); most preferably, however, theunsaturated copolymerizing component composed mainly of an acrylonitrilecomponent is absorbed onto a crystalline metal compound as the templatecompound to form a complex, which is subjected to solid-phasepolymerization reaction for high molecularization.

The template compound used in this case is preferably a crystallinemetal compound of Groups IIA to IIB of the Periodic Table, among whichthere may be mentioned halides, oxides, hydroxides, sulfides, nitrates,nitrites, sulfates, carbonates, thiosulfates, phosphates, aliphaticcarboxylates and aromatic carboxylates, with halides being particularlypreferred.

When the complex obtained by absorption onto the template compound asdescribed above participates in the solid-phase polymerization reaction,the crystalline metal compound has an orderly and arranged structure ofthe metal cation and its pairing counter anion, and the acrylonitrilecomponent and the unsaturated copolymerizing component can coordinatewith the metal cation via unpaired electrons on the oxygen atoms ornitrogen atoms of the carboxyl groups, amide groups or carboxylic acidester groups.

The arrangement of the acrylonitrile component and unsaturatedcopolymerizing component is determined by the order, sizes and interiondistances of the metal cation and its counter anion. The arrangementwill differ depending on the type of crystalline metal compoundselected, but preferably a halide of a metal of Groups IIa to IIB of thePeriodic Table is used as the template compound for isotacticstereocontrol.

As examples of such compounds there may be mentioned iron chloride,cobalt chloride, nickel chloride, manganese chloride, chromium chloride,anhydrous magnesium chloride, anhydrous calcium chloride, anhydrouslanthanum chloride, anhydrous yttrium chloride, iron bromide, cobaltbromide, nickel bromide, manganese bromide, chromium bromide, anhydrousmagnesium bromide, anhydrous calcium bromide, anhydrous lanthanumbromide, anhydrous yttrium bromide, iron iodide, cobalt iodide, nickeliodide, manganese iodide, chromium iodide, anhydrous magnesium iodide,anhydrous calcium iodide, anhydrous lanthanum iodide, anhydrous yttriumiodide, and the like. Two or more of these may also be used incombination, or there may be used a complex salt such as alum orhydrotalcite having two or more metal cations present in a singlecrystal system.

The crystal system of the metal compound is most preferably a hexagonalsystem and/or trigonal system. Most metal compounds of hexagonal andtrigonal systems adopt a layered structure on the macroscopic scale, andacrylonitrile components or unsaturated copolymerizing components becomeenclosed between the crystalline metal compound layers with the polargroups oriented in the same direction to produce a regularly orderedarrangement. Such hexagonal and/or trigonal metal compounds includecalcium bromide hexahydrate, calcium iodide, calcium iodide hexahydrate,cobalt (II) chloride, cobalt (II) bromide, cobalt (II) iodide, cobalt(II) iodide hexahydrate, cesium nitrate, cadmium chloride, cadmiumbromide, cadmium iodide, iron (II) chloride, iron (III) chloride, iron(II) bromide, iron (III) bromide, iron (II) iodide, potassium disulfide,potassium nitrite dihydrate, lithium iodide trihydrate, magnesiumchloride, magnesium bromide hexahydrate, magnesium hydroxide, manganese(II) chloride, manganese (II) bromide, sodium nitrite, nickel (II)chloride, tin sulfate dihydrate, titanium (II) chloride, titanium (III)chloride, vanadium (II) chloride, vanadium (II) bromide, vanadium (III)bromide and zinc chloride, among which iron (III) chloride, cobalt (II)chloride and magnesium chloride are preferred, and magnesium chloride isparticularly preferred.

The acrylonitrile component and unsaturated copolymerizing component(hereinafter both of these will be collectively referred to as “monomercomponent”) are contacted with the template compound to form a complex,and this step is preferably carried out in an inert gas atmosphere ofnitrogen or argon because if an oxygen-containing mixed gas such as airis used the radical growth ends may become inactivated, rendering itdifficult to finally obtain a carbon fiber precursor polymer with asufficient degree of polymerization.

The molar ratio of the monomer component and the crystalline metalcompound of Groups IIA to IIB of the Periodic Table (A/M) is preferablyat least 0.1 and less than 5.0, as this range gives the optimal amountof monomer component to coordinate with the template compound in orderto obtain a high molecular compound, and allows the stereoregularity ofthe obtained carbon fiber precursor copolymer to be further increasedsince there is no adverse effect due to excess monomer component.

The particle size of the crystalline metal compound is also important,and the particle size of the metal compound is preferably at least 1 μmand less than 100 mm, and more preferably at least 5 mm and less than 50mm, in order to obtain a carbon fiber precursor polymer having aviscosity-average molecular weight (hereinafter abbreviated as “Mv”) of50,000 or greater for an adequate spinning property.

If fine particles with a metal compound particle size of 1 μm or smalleris used, the Mv of the obtained carbon fiber precursor polymer will bebelow 50,000 and spinning will thus be extremely hampered. On the otherhand, the particle size is preferably not 100 mm or greater because themonomer component may infiltrate into the interior of the metal compoundand lengthen the time to completion of complex formation, while thecomplex formation itself may occur in a non-uniform manner.

The latter case should be avoided above all as it can lead to variationin the Mv during the subsequent solid-phase polymerization reaction.

The complex formed in the manner described above is transferred to anappropriate vessel under an inert gas atmosphere prior to thesolid-phase polymerization reaction.

Solid-phase polymerization reaction processes are largely of two types,one being thermal solid-phase polymerization employing a reactioninitiator capable of generating radicals by thermal decomposition, andthe other being electromagnetic solid-phase polymerization utilizingirradiation of radical generating electromagnetic waves.

Thermal solid-phase polymerization includes a method wherein thereaction initiator is dissolved in a small amount of an organic solventprior to addition and a method wherein a prepared solution of thereaction initiators in the monomer component is added to the crystallinemetal compound, with the latter method being considered the preferredmode from the standpoint of uniform distribution of the reactioninitiator. The addition may be accomplished by either a method ofspontaneous absorption of the complex in a stationary state or a methodof applying an appropriate degree of agitation to the complex, providedthat the stirring is not so vigorous as to break up the complex.

The reaction initiator of the invention may be any one of ordinarilyused as a reaction initiator for radical polymerization, and there maybe suitably used transition metal compounds capable of single-electronrelease to promote radical polymerization, including azo compoundsrepresented by azobisisobutyronitrile,2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),dimethyl-2,2-azobis(2-methylpropionate),1,1-(cyclohexane-1-carbonitrile), 2,2-azobis(2-methylbutyronitrile) and2,2-azobis[N-(2-propenyl)-2-methylpropionamide], organic peroxidesrepresented by benzoyl peroxide, oxidation-reduction reaction initiatorsrepresented by potassium peroxysulfate/sodium nitrite orN,N′-dimethylaniline/benzoyl peroxide combinations, and manganese (III)acetylacetonate, cobalt (II) acetylacetonate, pentacyanobenzyl cobaltateand iron (II) sulfate/hydrogen peroxide (Fenton's reagent).

On the other hand, electromagnetic solid-phase polymerization has theadvantage of requiring no addition of a reaction initiator sinceradicals are generated by irradiation of electromagnetic waves. Theelectromagnetic waves used may be any of sufficient energy to generateradicals in the monomer molecules, and there may be mentionedultraviolet rays, X-rays, y-rays, monochromatic visible light rays,natural sun rays, electron beams and the like.

The suitable temperature conditions for the solid-phase polymerizationreaction are −80° C. to 150° C. A temperature of below −80° C. may notonly drastically reduce the polymerization reaction rate, but will alsoincrease the energy consumption required for cooling. A temperature ofabove 150° C. may result in gaseous dissociation of the monomer from thecrystalline metal compound, making it impossible to obtain a carbonfiber precursor polymer with a satisfactory Mv.

The complex produced by the solid-phase polymerization reaction iscomposed of the crystalline metal compound and the carbon fiberprecursor monomer. The final carbon fiber precursor polymer cantherefore be obtained as the residue from elution of the metal compoundwith water, methanol, ethanol or the like.

The composition of the obtained polymer and the tacticity of thepolyacrylonitrile main chain may be quantified by ¹H-NMR and ¹³C-NMR.

The carbon fiber precursor polymer of the invention obtained by theproduction process described above may be spun by a conventionalpublicly known technique. The specific spinning method is notparticularly restricted and may be ordinary wet spinning, dry spinningor dry-wet spinning. According to the invention, the carbon fiberprecursor polymer filament obtained up to this point is referred to asthe carbon fiber precursor. Incidentally, flame retardation of theisotactic-rich PAN units sometimes proceeds partially due to heattreatment for stretching and the like during the spinning step, andthese modified structures are also encompassed within the scope of thecarbon fiber precursor of the invention.

The carbon fiber precursor of the invention is converted to carbonfibers by heating flame retardant treatment at a temperature of 150-300°C., heating carbonization treatment at 300-2000° C. in an inert gasatmosphere, and graphite growth at 2000-2500° C. The atmosphere for theflame retardant treatment may be an inert gas atmosphere such asnitrogen, but an active gas atmosphere such as air is preferred from thestandpoint of shortening the flame retardant treatment time. A lowcarbonization temperature of below 300° C. may result in the problem ofreduced elasticity of the obtained carbon fibers. The carbon fibers mayoptionally be further subjected to surface treatment or oil coating orsizing treatment, as necessary.

The reason for the more rapid and lower temperature flame retardanttreatment of the carbon fiber precursor polymer and carbon fiberprecursor of the invention is believed to be as follows.

Specifically, as explained above, the flame retardant reaction occurswith intramolecular cyclization of adjacent nitrile groups in thestructural chain, and therefore an isotactic structure wherein thenitrile groups are in a meso configuration is advantageous from apositional standpoint for cyclization of the adjacent nitrile groups, sothat the reaction proceeds with a lower activation energy. Consequently,the flame retardant treatment can be carried out at a lower temperaturewith an isotactic structure.

In addition, since the carbon fiber precursor has a 3/1 helicalstructure induced by its isotacticity, it forms straight-chain fusedpyridine rings, or a polynaphthylidine skeleton, during the flameretardant step.

Thus, the size of the hexagonal plane layer which grows at the stage ofcarbonization or graphitization is larger than achieved using aconventional carbon fiber precursor with an atactic structure, and thestrength of the obtained carbon fibers is therefore increased.

EXAMPLES

The present invention will now be explained in greater detail throughreference examples and examples, with the understanding that theinvention is in no way restricted thereby.

The monomer conversion rate during polymerization and the compositionsof the obtained polymers were determined by ¹H-NMR, and thestereoregularity (tacticity) of the polymers was quantified by ¹³C-NMR(270 MHz, DMSO-d6 solvent JNR-EX-270 by Nihon Denshi Datum Co., Ltd.),to determine the isotactic triad content (mm %), syndiotactic triadcontent (rr %) and heterotactic triad content (mr %).

Example 1

A 50 g portion of hexagonal anhydrous magnesium chloride having aparticle size of 10-30 mm was loaded as the template compound into athree-necked flask under a dry nitrogen stream, and kept in an ice bathat below 10° C.

A separately prepared three-necked flask was substituted with nitrogen,and then 34.6 ml of acrylonitrile, 2.0 ml of methyl acrylate, 1.2 ml ofdibutyl itaconate and 0.25 g of azobisisobutyronitrile were combinedtherein as the monomer solution.

The mixture was then added to the three-necked flask containing theanhydrous magnesium chloride, and allowed to thoroughly absorb toprepare an A/M=1/1 complex.

Next, the three-necked flask was set in a hot-air circulating drier for12 hours of solid-phase polymerization at 70° C. After the solid-phasepolymerization, the complex was poured into methanol and the anhydrousmagnesium chloride was removed by solvent extraction to yield aninsoluble carbon fiber precursor copolymer in methanol, which was thenfiltered out and collected, washed with ion-exchanged water and acetonein that order, and then dried under reduced pressure overnight at 40° C.

The obtained carbon fiber precursor copolymer yield was 18.2 g (65.4%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 94.5%, 2.4% and 3.1% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively.

¹³C-NMR measurement was carried out to determine the tacticity,confirming a high degree of isotacticity with mm/mr/rr=68.3/21.3/10.4.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 2.04.

Example 2

A 50 g portion of hexagonal anhydrous magnesium chloride having aparticle size of 10-30 mm was loaded as the template compound into athree-necked flask under a dry nitrogen stream, and kept in an ice bathat below 10° C.

A separately prepared three-necked flask was substituted with nitrogen,and then 34.6 ml of acrylonitrile, 2.0 ml of methyl acrylate and 1.2 mlof dibutyl itaconate were combined therein as the monomer solution. Themixture was then added to the three-necked flask containing theanhydrous magnesium chloride, and allowed to thoroughly absorb toprepare an A/M=1/1 complex.

Next, the three-necked flask and a 300 ml screw-necked glass bottle wereplaced in a nitrogen-substituted globe box and the complex wastransferred from the three-necked flask to the screw-neck glass bottle.The screw-neck glass bottle containing the complex was set in a γ-rayirradiating apparatus with a ⁶⁰Co ray source, for electromagneticsolid-phase polymerization at a dose of 10 KGy. The obtained carbonfiber precursor copolymer yield was 16.6 g (59.5%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 94.5%, 2.6% and 2.9% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, confirming a high degree of isotacticity withmm/mr/rr=68.1/21.5/10.4, The intrinsic viscosity [η] measured inN,N′-dimethylformamide at 35° C. was 2.96.

Example 3

The same procedure was carried out as in Example 1, except thathexagonal anhydrous cobalt chloride was used instead of anhydrousmagnesium chloride.

After completion of the solid-phase polymerization, the complex waspoured into 5 wt % diluted hydrochloric acid and the anhydrous cobaltchloride was removed by extraction to yield an insoluble carbon fiberprecursor copolymer in the diluted hydrochloric acid which was thenfiltered out and collected. It was subsequently washed withion-exchanged water and acetone in that order and then dried underreduced pressure overnight at 40° C.

The obtained carbon precursor copolymer yield was 11.9 g (42.7%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 93.3%, 2.8% and 3.9% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, confirming a high degree of isotacticity withmm/mr/rr=85.1/13.1/1.8.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 1.67.

Example 4

The same procedure was carried out as in Example 3, except thathexagonal anhydrous iron chloride was used instead of anhydrous cobaltchloride.

The obtained carbon precursor copolymer yield was 14.4 g (51.6%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 95.7%, 2.6% and 1.7% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, confirming a high degree of isotacticity withmm/mr/rr=81.3/13.9/4.8.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 1.46.

Example 5

The same procedure was carried out as in Example 1, except that 42 g oforthorhombic hexagonal beryllium chloride was used instead of anhydrousmagnesium chloride.

The obtained carbon precursor copolymer yield was 17.1 g (61.3%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 95.4%, 2.9% and 1.7% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, which was mm/mr/rr=38.0/38.2/23.8.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 1.98.

Example 6

The same procedure was carried out as in Example 1, except that 50 g ofanhydrous magnesium chloride, 103.8 ml of acrylonitrile, 6.0 ml ofmethyl acrylate, 3.6 ml of dibutyl itaconate and 0.75 g ofazobisisobutyronitrile were combined, for A/M=3/1.

The obtained carbon precursor copolymer yield was 82.2 g (91.8%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 95.9%, 2.5% and 1.6% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, which was mm/mr/rr=38.2/38.0/23.8.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 2.62.

Example 7

The same procedure was carried out as in Example 1, except that finepowdery magnesium chloride with a particle size of 1 μm or smaller wasused.

The obtained carbon precursor copolymer yield was 25.6 g (91.8%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 95.5%, 2.7% and 1.8% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively. ¹³C-NMR measurement was carried out to determine thetacticity, which was mm/mr/rr=67.9/21.6/10.5.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 1.95.

Example 8

The same procedure was carried out as in Example 1, except thatacrylonitrile alone was used as the starting material, without methylacrylate or dibutyl itaconate.

The obtained carbon precursor copolymer yield was 18.8 g (67.7%).

¹³C-NMR measurement was carried out to determine the tacticity, whichwas mm/mr/rr=68.4/24.4/7.2.

The intrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.was 1.81.

Comparative Example 1

Polymerization was conducted under the same conditions as in Example 1,except that no anhydrous magnesium chloride was added as a templatecompound.

The obtained carbon precursor copolymer yield was 21.9 g (78.5%).

The copolymer composition was estimated by ¹H-NMR measurement,indicating contents of 95.3%, 2.9% and 1.8% for the acrylonitrilecomponent, methyl acrylate component and dibutyl itaconate component,respectively.

¹³C-NMR measurement was carried out to determine the triad tacticity,which was mm/mr/rr=27.0/50.4/22.6, confirming that a substantiallyatactic carbon fiber precursor copolymer had been obtained. Theintrinsic viscosity [η] measured in N,N′-dimethylformamide at 35° C.using a Ubbelohde viscometer was 1.83.

The isotactic-rich carbon fiber precursor copolymers of the examples hadtop temperatures for the exothermic peak of cyclization reaction duringthe flame retardant treatment which were shifted toward the lowertemperature end compared to the more atactic comparative example, withincreased peak mesial magnitude and reduced heat generation.

These results suggest that an isotactic-rich carbon fiber precursorpolymer according to the invention allows flame retardant treatment tobe carried out in a lower temperature range, while the large mesialmagnitude and low heat generation suggest more gentle progression of theflame retardant reaction.

A major effect is therefore exhibited by the carbon fiber precursorpolymer and carbon fiber precursor with no fusion or thermaldecomposition between carbon fibers and excellent flame retardanttreatment characteristics.

1. A carbon fiber precursor polymer which is composed of a polymercomprising 50 wt % or greater of an acrylonitrile component, wherein theisotactic triad proportion of the acrylonitrile structural chaincomposed of the acrylonitrile component is 35 mole percent or greaterbased on the total triad proportion of the acrylonitrile structuralchain composed of the acrylonitrile component.
 2. A carbon fiberprecursor polymer according to claim 1, which comprises a copolymerfurther composed of an acrylic acid-based compound component and anacrylic acid ester-based compound component as the main copolymerizingcomponents in addition to the acrylonitrile component, wherein saidacrylonitrile component constitutes at least 80 wt % of the copolymerand the total weight percentage of the acrylic acid-based compoundcomponent and the acrylic acid ester-based compound component is greaterthan 0% and less than 20%.
 3. A carbon fiber precursor polymer accordingto claim 1, wherein the isotactic triad proportion of the acrylonitrilestructural chain composed of the acrylonitrile component is at least 65mole percent.
 4. A carbon fiber precursor polymer according to claim 1,wherein the intrinsic viscosity of the polymer is between 0.1 and 10.0.5. A carbon fiber precursor obtained by spinning a polymer according toclaim
 1. 6. A flame retardant carbon fiber precursor obtained by heattreating a carbon fiber precursor according to claim 5 at 200-300° C. inthe presence of oxygen.
 7. A process for production of a carbon fiberprecursor polymer, which yields a carbon fiber precursor polymercomposed of a polymer comprising 50 wt % or greater of an acrylonitrilecomponent, wherein the isotactic triad proportion of the acrylonitrilestructural chain composed of the acrylonitrile component is 35 molepercent or greater based on the total triad proportion of theacrylonitrile structural chain composed of the acrylonitrile component,by using an unsaturated copolymerizing component composed mainly ofacrylonitrile as a template compound, absorbing it into a crystallinemetal compound to form a complex, and subjecting the complex tosolid-phase polymerization reaction for high molecularization.
 8. Aprocess for production of a carbon fiber precursor polymer according toclaim 7, wherein the crystalline metal compound is a compound of a metalof Groups IIA to IIB of the Periodic Table.
 9. A process for productionof a carbon fiber precursor polymer according to claim 7, wherein saidmetal compound is a halide.
 10. A process for production of a carbonfiber precursor polymer according to claim 7, wherein said metalcompound is a hexagonal and/or trigonal metal compound.
 11. A processfor production of a carbon fiber precursor polymer according to claim10, wherein said metal compound has a layer structure of at least onecompound selected from the group consisting of cadmium iodide, cadmiumchloride and cadmium sulfide type compounds.
 12. A process forproduction of a carbon fiber precursor polymer according to claim 7,wherein the solid-phase polymerization reaction is carried out by addinga radical polymerization initiator to said complex and heating themixture.
 13. A process for production of a carbon fiber precursorpolymer according to claim 7, wherein the solid-phase polymerizationreaction is carried out by irradiating said complex with electromagneticwaves.
 14. A process for production of a carbon fiber precursor polymeraccording to claim 8, wherein the molar ratio of the unsaturatedcopolymerizing component composed mainly of acrylonitrile and thecrystalline metal compound (A/M) is between 0.1 and 5.0.
 15. A processfor production of a carbon fiber precursor polymer according to claim 7,wherein the particle size of the crystalline metal compound is between 1μm and 100 mm.
 16. A process for production of a carbon fiber precursorpolymer according to claim 7, wherein the particle size of thecrystalline metal compound is between 5 mm and 50 mm.
 17. A process forproduction of a carbon fiber precursor polymer according to claim 7,wherein the solid-phase polymerization reaction temperature is between−80° C. and 150° C.